The present invention relates to the stereo and audio industries and, more particularly, to the field of audio amplifiers for amplifying audio and related methods.
Over the years, the stereo and audio industries have grown dramatically. As additional capabilities of the various audio and stereo equipment has advanced, a continual cost pressure of new equipment from consumers and the increased worldwide competition has forced prices to down over the years for audio and stereo equipment. This audio and stereo equipment, for example, includes audio amplifiers, power boosters, power supplies, receivers, transmitters, radios, clocks, tuners, speakers, tape, compact disc, and various players, and various other equipment as understood by those skilled in the art.
In the power audio amplifier field, however, many advancements have focused on improved techniques for generation of high acoustic power and yet have high bandwidth and low distortion. Also, improvements have been made in providing power or supplying power to audio amplifiers. These power amplifiers conventionally use two different power sources. One from a high voltage source and another from a low voltage source. A switching transistor is often used to change between the low and high voltage sources. The audio signal applied to the speaker is detected, and when the level of audio signal exceeds a preselected level, the switching transistor is so turned as to supply power from the high voltage source. When the level of the audio signal is below the preselected level, the switching transistor is so turned as to supply power from the low voltage source. High levels of power, especially for long periods of time or in very high surges, can overheat and severely damage the transistors and many of the other electronic components of these audio amplifiers.
To address some of these problems, power amplifiers have been developed with temperature controls which attempt to prevent the transistors and other electronic components from overheating. Examples of such power amplifiers can be seen in U.S. Pat. No. 5,818,301 by Higashiyama et al. titled xe2x80x9cPower Amplifier Arrangement Of A Plural Power Supply Switching Typexe2x80x9d and U.S. Pat. No. 5,331,291 by D""Agostino et al. titled xe2x80x9cCircuit And Method For Adjusting The Bias Of An Amplifier Based Upon Load Current And Operating Temperature.xe2x80x9d Such power amplifiers, however, fail to take into account power surges which can arise, particularly in start up, which can quickly damage the transistors and other electronic components.
To address these power surge problems, circuits have been developed which detect abnormal voltage levels and cut off portions of a power amplifier circuit. An example of such a circuit can be seen in U.S. Pat. No. 5,847,610 by Fujita titled xe2x80x9cProtection Circuit For An Audio Amplifier.xe2x80x9d Such power circuits do little to address start up problems and do little to discriminate or recognize true or false power surge problems.
With the foregoing in mind, the present invention advantageously provides an audio amplifier controller for an audio amplifier and associated methods which limits in-rush current during start up and slowly ramps up to a high power and amplifier state. The present invention also advantageously provides an audio amplifier controller which in combination allows for soft start capabilities, power discrimination capabilities, and thermal monitoring capabilities to enhance protection for power audio amplifiers during various power surge and temperature increasing conditions. The present invention additionally advantageously provides an audio amplifier controller which monitors the current output of the amplifier to protect speakers or other devices by disconnecting the load to the output circuits during high current conditions and then continues to monitor the current output to resume normal conditions if desirable. The present invention yet also provides an audio amplifier controller for an audio amplifier which protects the amplifier from going into and remaining in a circuit protection mode by continuously monitoring for normal current conditions. The present invention further advantageously provides an audio amplifier having an audio controller and associated methods which detects voltage level changes by frequency changes and voltage nulls. The present invention still further provides an alternating current soft start circuit which advantageously limits inrush current and allows a slow ramp up of power to a high power on-state by sensing frequency and voltage nulls.
More particularly, the present invention provides an audio amplifier power and temperature controller which preferably includes power receiving means for receiving power from a power source to an audio amplifier and power condition switching control means responsive to the power receiving means for switching components of an audio amplifier during a plurality of power conditions. The power condition switching control means preferably includes soft starting means responsive to the power receiving means for limiting inrush current from the power receiving means and for slowly ramping up to an audio amplifier on-state, thermal status monitoring and controlling means for monitoring thermal status of operating values of audio amplifier components and responsively decreasing power to the audio amplifier components to protect the audio amplifier components against damage caused by excess heat and for responsively increasing power when the audio amplifier components return to normal thermal operating conditions, and output monitoring means for monitoring current output circuits of the audio amplifier to protect an audio amplifier during a high current condition when connected to the audio amplifier by disconnecting a load to the current output circuits and reconnecting the load to the current output circuits when normal operating current conditions resume.
The present invention additionally includes a alternating current (xe2x80x9cACxe2x80x9d) soft starting circuit which preferably has a power level detecting circuit responsive to an alternating current source and positioned to detect voltage changes by sensing frequency changes and voltage null points and a micro-controller responsive to the power level detection circuit to monitor low power conditions and high power conditions to limit inrush current during high power condition from the alternating current source and to slowly ramp up to high power on-state condition. The AC soft start circuit can also include the micro-controller having wave analyzing means for analyzing sinusoidal waves of the alternating current source detected by the power level detection circuit to determine a voltage null so that the soft start function allows a power on-state to be initiated just prior to a voltage null and to gradually ramp up to a the high power on-state condition.
The present invention also includes methods of controlling power to an audio amplifier. A method preferably includes receiving power from a power source to an audio amplifier and switching components of an audio amplifier during a plurality of power conditions. The step of switching components preferably includes limiting inrush current from the power source, slowly ramping up to an audio amplifier on-state, monitoring thermal status of operating values of audio amplifier components, responsively decreasing power to the audio amplifier components to protect the audio amplifier components against damage caused by excess heat, and responsively increasing power when the audio amplifier components return to normal thermal operating conditions.